Review on High Pressure Hand-held Shower Head with ON/Off Switch - 3 Modes, Handheld Shower Head with Hose, Chrome Finish by Pete Brown

The shower head is supplied with a non-return valve. The manual doesn't say how to install it. There are instructions on the box but I can't tell where to put them. At the tip that enters the hose, or at the end next to the head itself. Also, the check valve has two sides. They don't say which side goes where. When installed backwards, it will stop the flow of water. The customer does not have to find this out through trial and error. I searched the internet. Many places explain what a check valve does. I haven't found one that explains these installation details. UPDATE: The manufacturer replied to the email and gave me more details. After you assemble it, it is a good shower head.